As the world's population continues to grow, its transportation demands are likewise rapidly increasing. Automobile usage is on the rise worldwide with some estimates reporting over 1 billion vehicles on the world's roads today and 2 billion by the year 2035. These estimates include passenger cars, light-, medium-, and heavy-duty trucks, and buses.
In many parts of the world, electric vehicles (EV) and hybrid-electric vehicles (HEV) have become feasible alternatives to traditional internal combustion engine (ICE) vehicles. This is especially true is some developing countries and in some emerging markets where large segments of population are rising in socio-economic level, and many more people are thus able to afford EV and HEV vehicles for both personal and commercial use.
EV/HEV powertrains, while quieter than internal combustion engines, can still produce unwanted noises which may cause annoyance to the occupants of a vehicle. EVs, in particular, tend to emit disturbing sounds such as high-pitched tones or “whine”. These sounds can be very tonal in nature and are typically in a frequency range of 500 Hz to 4 kHz. The perceptibility and annoyance of these tones is dependent on their frequency and amplitude relative to other noise within the vehicle. Unfortunately, this frequency range is outside the range that can be effectively mitigated using active noise control. Passive noise and vibration dampening methods can be effective, but in most cases do not eliminate the whine entirely from the cabin. Therefore, there is a need for an improved way of masking undesirable vehicle powertrain tones.
Similar reference numerals may have been used in different figures to denote similar components.